Beneficial effect of low BN additive on densification and mechanical properties of hot-pressed ZrB2–SiC composites

Abstract

The incorporation of 1 wt% hexagonal BN (hBN) into ZrB2–30 vol% SiC could noticeably better the fracture toughness, hardness, and consolidation behavior of this composite. This research intended to scrutinize the effects of various amounts of hBN (0–5 wt%) on different characteristics of ZrB2–SiC materials. The hot-pressing method under 10 MPa at 1900 °C for 120 min was employed to sinter all designed specimens. Afterward, the as-sintered samples were characterized using X-ray diffractometry (XRD), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS), and Vickers technique. The hBN addition up to 1 wt% improved relative density, leading to a near fully dense sample; however, the incorporation of 5 wt% of such an additive led to a composite containing more than 5% remaining porosity. The highest Vickers hardness of 23.8 GPa and fracture toughness of 5.7 MPa.m1/2 were secured for the sample introduced by only 1 wt% hBN. Ultimately, breaking large SiC grains, crack bridging, crack deflection, crack branching, and crack arresting were introduced as the chief toughening mechanisms in the ZrB2–SiC–hBN system.

Challenges toward applying UHTC-based composite coating on graphite substrate by spark plasma sintering

“…Many efforts have been done to increase the oxidation resistance of diborides. These studies showed that the addition of SiC to ZrB2 greatly increases oxidation resistance at high temperatures [36][37][38][39][40][41][42][43]. Thermodynamic calculations of the oxidation of ZrB2-SiC composites showed that the formation of a SiC-rich layer, a Zr-rich oxidized layer and a SiC-depleted ZrB2 layer due to active oxidation of SiC decreased the oxidation rate [44].…”

Influence of TiN addition on densification behavior and mechanical properties of ZrB2 ceramics

“…Hence, applying high pressures and elevated temperatures is necessary to obtain a fully dense ZrB 2 sample, which encourages the growth of grains and results in a significant decline in fracture toughness. To overcome such problems, several research works have suggested the selection of suitable consolidation techniques and/or activating the toughening and sintering mechanisms utilizing the addition of additives [6][7][8]. Among spark plasma sintering (SPS), pressureless sintering (PS), reactive hot pressing (RHP), and hot pressing (HP) [9,10], as the sintering techniques for the fabrication of UHTCs, the first one is a newly developed route that utilizes direct current pulsing and external mechanical pressure to densify the materials synchronously [11][12][13].…”

On the oxidation behavior of ZrB2–SiC–VC composites

“…The ZrB 2 itself has high oxidation resistance because of adherent and dense oxide scale formation 16,17 . The resistance to oxidation also alters by the addition of other compounds.…”